In the 3rd Generation Partnership Project (3GPP), defined are four scenarios for Coordinated Multi-Point (COMP) transmission, wherein the scenario 4 means that transmission points including Macro Site and Remote Radio Head (RRH,) within a macro station area share an identical Cell Identity, and this architecture is also referred to as a Distributed Antenna System (DAS).
In the DAS system, in order that the receiving powers of different User Equipments (UE) upon reaching a base station (eNB, evolved Node B) are roughly on the same level to avoid inter-user interference caused by the near-far effect, uplink power control is generally adopted for the UE. In Long Term Evolution (LTE) R-10 standards, the transmitting powers of a Physical Uplink Shared Channel (PUSCH), a Physical Uplink Control Channel (PUCCH) and a Sounding Reference Signal (SRS) are determined according to a Path Loss (PL) estimated on the UE side, specifically shown in formula (1) below:PL=ReferenceSignalPower−RSRP  (1)where ReferenceSignalPower is a reference signal power defined by the base station, and the UE acquires the reference signal power through a cell specific high-layer signaling; and RSRP is a Reference Signal Receiving Power measured by the UE at a Common Reference Signal (CRS) antenna Port0 or Port1.
In present scenario 4, the path loss is measured on the basis of the CRS by adopting the aforementioned formula (1), wherein CRS Port0 and Port1 may be virtually mapped to antennas of respective RRHs for transmission, and the UE may receive CRSs transmitted from the respective RRHs.
The RSRP is a superposition of energy of measurement reference signals from the respective RRHs, which are received by the UE, as shown in formula (2) below:
                              R          ⁢                                          ⁢          S          ⁢                                          ⁢          R          ⁢                                          ⁢          P                =                  10          ⁢                                          ⁢                                    log              10                        ⁡                          (                                                ∑                                      i                    =                    0                                                        N                    -                    1                                                  ⁢                                  10                                                            (                                                                        P                          i                                                -                                                  PL                          i                                                                    )                                        10                                                              )                                                          (        2        )            
The path loss may be obtained as
                                                                        P                ⁢                                                                  ⁢                L                            =                            ⁢                                                10                  ⁢                                                            log                      10                                        ⁡                                          (                                                                        ∑                                                      i                            =                            0                                                                                N                            -                            1                                                                          ⁢                                                  P                          i                                                                    )                                                                      -                                  10                  ⁢                                                            log                      10                                        ⁡                                          (                                                                        ∑                                                      i                            =                            0                                                                                N                            -                            1                                                                          ⁢                                                  10                                                                                    (                                                                                                P                                  i                                                                -                                                                  PL                                  i                                                                                            )                                                        10                                                                                              )                                                                                                                                              =                            ⁢                              10                ⁢                                                      log                    10                                    (                                                                                    ∑                                                  i                          =                          0                                                                          N                          -                          1                                                                    ⁢                                              P                        i                                                                                                            ∑                                                  i                          =                          0                                                                          N                          -                          1                                                                    ⁢                                              10                                                                              (                                                                                          P                                i                                                            -                                                              PL                                i                                                                                      )                                                    10                                                                                                      )                                                                                        (        3        )            where Pi is transmitting power of each RRH, and PLi is path loss from each RRH to the UE.
Thus, it can be seen that, because the receiving power is the superposition of the energy of the signals from different RRHs, the path loss measured on the basis of the CRS by using the aforementioned formula (3) is a nonlinear superposition of path losses from all the RRHs to the UE. The actual uplink target RRH is one of the RRHs or a set of multiple RRHs rather than all the RRHs. In such case, the actual path loss compensation in respect of the target RRH does not match the measured path loss, so that the calculation of the uplink transmitting power is inaccurate, and then the performance of uplink transmission is affected.